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Endocrine System
N/A
39
Anatomy
Undergraduate 1
02/24/2009

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Term
Endocrine System
Definition
System of organs and cells that communicate with other cells by releasing hormones into the blood.

Function - coordinate & regulate processes of the body: metabolic rate, reproductive processes, development, growth, water/electrolyte balance, mood, etc.

Important in the maintenance of homeostasis.
Term
Negative Feedback Mechanisms
Definition
Keeps conditions near a set point. When a condition is beyond an acceptable range, processes are activated to bring it back.

ex. (non-endocrine) Regulation of body temperature. Low temp - vasoconstriction and shivering. High temp - vasodilation and sweating.

ex. (endocrine) Regulating blood glucose level. Normal: 70-110 mg/dL. Too high - pancreas releases insulin; insulin reduces blood glucose. Too low - pancreas releases glucagon; glucagon raises blood glucose.
Term
Positive Feedback Mechanisms
Definition
Self-amplifying cycle in which a physiological change leads to an even greater change in the same direction.

ex. Progression of labor - baby's head puts pressure on cervix; stimulates hypothalamus to release oxytocin; oxytocin stimulates uterine contractions; contractions put more pressure on cervix; repeat.
Term
Hormone
Definition
Organic chemicals released into the bloodstream to regulate the activity of cells in another tissue or organ.
Term
Steroid Hormones
Definition
Made from cholesterol.

ex. Cortisol, estrogen, testosterone.
Term
Monoamines
Definition
In most cases, made from a single, modified amino acid.

ex. Dopamine, epinephrine, serotonin, thyroid hormones (2 tyrosines).
Term
Peptide Hormones
Definition
Made from chains of amino acids.

ex. Insulin, growth hormone, oxytocin.
Term
Hormone: Release & Activity
Definition

1) Endocrine gland receives signal from neuron or another gland's hormone.

2) Hormone is released into blood stream.

3) Hormone travels body, binding receptors on/in target cells.

4) Hormone binds to cell receptor: Steroid & others can go through plasma membrane; have receptors inside the cell, many inside nucleus (associated with chromatin). Others bind to plasma membrane receptors.

Effect - may change rate of reactions, stimulate target cell to take up/release materials, regulate DNA transcription, and protein synthesis.

Term
Hormones that are needed at a steady level are...
Definition
...regulated by negative feedback inhibition. The presence of the hormone inhibits the release of more hormone.

ex. Hypothalamus makes TRH; TRH makes pituitary gland release TSH; TSH makes thyroid gland release TH; presence of TH inhibits release of TRH > inhibits release of TSH > inhibits release of TH.
Term
Hormones that are needed under certain conditions are...
Definition
...regulated by negative feedback inhibition. The activity of the hormone changes the initial condition, inhibiting the release of more hormone. ex. High blood glucose stimulates insulin release; insulin causes cells to take in glucose; lowered blood glucose ceases insulin release.
Term
Hypothalamus
Definition
Located in the brain. Produces releasing hormones that are important for regulating the release of pituitary gland hormones. Also produces OT and ADH, which are stored in/released from the posterior lobe of the pituitary gland.
Term
Pituitary Gland
Definition
Connected to the hypothalamus and consists of two lobes: anterior and posterior lobes. Anterior Lobe - controlled by hypothalamus' releasing hormones. Releases GH, FSH, LH, TSH, ACTH, & PRL. Posterior Lobe - Stores and releases hormones made in the hypothalamus: OT & ADH.
Term
Thyroid Gland
Definition
Largest endocrine gland. Wrapped around trachea, inferior to the larynx. Releases T3 & T4, and calcitonin.
Term
Parathyroid Glands
Definition
Four small glands on posterior side of thyroid. Releases PTH.
Term
Pancreas
Definition
Mostly an exocrine digestive gland. Pancreatic islets, clusters of endocrine cells, create and release insulin, glucagon, and somatostatin (also paracrine).
Term
Paracrine Secretions
Definition
Refers to a hormone that is released into the gland's surrounding tissue instead of the bloodstream. Affects target cells near the gland.
Term
Adrenal Glands
Definition
Located on superior surface of kidneys. Separated into two parts: Adrenal Medulla - Inner part controlled by autonomic nervous system; releases epinephrine/norepinephrine. Adrenal Cortex - Outer part; releases aldosterone, cortisol, estrogens, and androgens.
Term
Ovaries
Definition
Produce ova; release estrogens and progesterone.
Term
Testes
Definition
Produce sperm; release testosterone.
Term
FSH
Definition

Follicle-stimulating hormone (peptide). Released by anterior lobe of pituitary. Targets: Ovaries - stimulates development of ova and follicles that contain them. Testes - stimulates sperm production.

 

[level is higher after menopause]

Term
LH
Definition

Luteinizing hormone (peptide). Released by anterior lobe of pituitary. Targets: Ovaries - stimulates ovulation; stimulates release of estrogen and progesterone (important to pregnancy). Testes - Stimulates release of testosterone.

 

[LH level peaks before menstruation and in the middle of the cycle (ovulation)]
[ovulation test kits detect LH to predict fertility]

Term
TSH
Definition

Thyroid-stimulating hormone or thyrotropin (peptide). Released by anterior lobe of pituitary. Stimulates growth of thyroid gland and release of thyroid hormone.

 

[TSH levels are tested to see if a person has too much or too little thyroid hormone]
[only 3 amino acids long]

Term
ACTH
Definition

Adrenocorticotropic hormone or corticotropin (peptide). Released by anterior lobe of pituitary. Stimulates adrenal cortex of adrenal glands to secrete their hormones, especially cortisol. Central to body's response to stress.

 

[also triggers release of GH]
[plays a role in the body’s response to stress]
[leads to changes in metabolism of carbs, fats, and proteins, see effects of cortisol]

Term
PRL
Definition

Prolactin (peptide). Levels rise during pregnancy, and after birth it stimulates mammary glands to synthesize milk. In males it makes testes more sensitive to LH; indirectly enhancing release of testosterone.

 

[increases testosterone secretion in men]
[casues the feeling of satisfaction following sex]

Term
GH
Definition

Growth hormone or somatotropin (peptide). Generally promotes mitosis and cellular differentiation: widespread tissue growth. Especially bone, cartilage, muscle, and fat. Directly stimulates tissues, but it also causes the liver and other tissues to produce growth stimulants (IGF-I & II, somatomedins). Increases protein synthesis and metabolism of fats.

 

[1000x more GH produced than any other pituitary hormone]
[many controversial uses: MS, fibromyalgia, Crohn’s disease, aging, obesity, etc]
[very short half-life of 6-20 minutes]
[high protein meals increase GH, high carb meal suppress GH]

Term
OT
Definition

Oxytocin (peptide). Causes smooth muscle of the uterus to contract, helping to expel the infant during labor. Causes mammary glands to squeeze milk into the ducts and to the nipple.


[Pitocin given to induce labor is a brand name for synthetic oxytocin]

[OT in the brain can cause sexual arousal, maternal behavior, and increased trust]

Term
ADH
Definition

Antidiuretic hormone or vasopressin (peptide). Acts on kidneys, increasing water retention, reducing urine volume, and helps prevent dehydration.

 

[causes vasoconstriction at high concentrations]
[functions as a neurotransmitter when released into junctions between neurons]
[some tumors and infections lead to increased levels of ADH]

Term
TH
Definition

Thyroid hormone (monoamine). Refers to both T3 and T4. Released in response to TSH. Primarily increases the body's metabolic rate. Increases oxygen consumption; has calorigenic effect (heat production); increases appetite, breakdown of carbs, fats, and protein for fuel; promotes alertness, bone growth and remodeling, development of skin, hair, nails, and teeth.

 

[increases oxygen use, heart/respiratory rate, appetite, alertness, bone growth, body heat]
[stimulates pituitary gland to release GH]
[iodine is required to make the thyroid hormone]
[too much (hyperthyroidism) or too little (hypothyroidism) thyroid hormone is a problem]

Term
Calcitonin
Definition

(peptide) Released by thyroid when blood calcium is high. Promotes bone growth to store calcium.

 

[prevents bone loss in pregnant and lactating women]
[very important in children but doesn’t have much effect on adults]
[may use calcitonin from fish as a future treatment for osteoarthritis]
[calcitonin structure is 32 amino acids that form a single alpha helix]

Term
PTH
Definition

Parathyroid hormone (peptide). Released by parathyroid in response to hypocalcemia. Raises blood calcium by: promoting calcitriol (form of vitamin D3) synthesis, which promotes intestinal absorption of calcium; inhibiting urinary calcium secretion; indirectly stimulating osteoclasts to reabsorb calcium from bones.

 

[increases synthesis of calcitriol (vitamin D) to absorb more calcium]
[may be removed with the thyroid gland in cases of hyperthyroidism, causes drop in Ca]
[binds to receptors in the membrane and activates second messenger system in cell]

Term
Insulin
Definition

(peptide) Released by pancreas in response to high blood glucose. Increases uptake to glucose (and other nutrients) into cells, use of glucose, and storage of glucose (glycogen).

 

[two men who discovered how to extract insulin received the 1923 Nobel prize]
[insulin means “island” in latin, referring to the islets of Langerhans]
[not producing insulin or resistance to insulin causes diabetes]
[binds to receptors in the membrane and brought in by receptor-mediated endocytosis]

Term
Glucagon
Definition
(peptide) Released by pancreas in response to low blood glucose. Stimulates gluconeogenesis in the liver, glycogenolysis, and the release of glucose into circulation. Stimulates fat catabolism and the release of free fatty acids (FFA) to spare glucose for brain. Promotes cellular intake of amino acids after high protein meal, providing raw material for gluconeogenesis.
Term
Epinephrine/Norepinephrine
Definition

(monoamine) Released from adrenal medulla in response to the activation of the sympathetic nervous system. Increases heart rate, breathing, blood pressure, and decreases digestion in preparation for fight-or-flight.

 

[also act as neurotransmitters, also known as adrenaline/noradrenaline]
[increase alertness and anxiety, decrease insulin secretion]
[epinephrine can treat bronchial asthma and acute allergies]
[epinephrine can be injected directly into a stopped heart to restart the heartbeat]

Term
Aldosterone
Definition

(steroid) Released by adrenal cortex. Stimulates kidneys to retain sodium and excrete potassium. Maintains blood pressure/volume.

 

[pregnant women may have higher levels of aldosterone]
[may be an important supplement to the action of coritsol]
[helps regulate water balance and urine output]
[loss of aldosterone can lead to death within days]

Term
Cortisol
Definition

(steroid) Released by adrenal cortex. Adapts the body to long term stress, increases blood pressure and blood glucose level, anti-inflammatory effect helps repair tissues, but suppresses immune system. Stimulates gluconeogenesis and use of alternative energy sources

[used to treat many conditions – rheumatoid arthritis, depression, stress, trauma,etc]

[after long stress, cortisol levels don’t return to normal, causes chronic stress]

Term
Estrogens & Androgens
Definition

(steroid) Released by adrenal cortex. Promotes growth of pubic and axillary hair, bone growth, sex drive, and male prenatal development.

 

[this is the source if testosterone in women and estrogen in men]

[androgen is required for a male fetus to develop male genetalia]

[insensitivity to androgen may cause infertility and intersexuality]

Term
Estradiol
Definition

(steroid) Estrogen released by ovaries. stimulates development of female reproductive organs & secondary sex characteristics; stimulates bone growth.

 

[estrogen treatment can increase the risk of breast cancer, heart disease, and stroke]

[50% of breast cancers depend on estrogen for continued growth]

Term
Progesterone
Definition

(steroid) Released by ovaries. Regulates the menstrual cycle and pregnancy.

 

[increases energy and calms anxiety]

[increases the core body temperature during ovulation]

[used to support difficult pregnancies or to prevent pregnancy in birth control pills]

[prepares mammary glands for lactation]

Term
Testosterone
Definition

(steroid) Released by testes. Stimulates development of male reproductive organs & secondary sex characteristics; stimulates bone growth.

 

[increases energy, red blood cells, libido, aggression]

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